1. Field of the Invention
The invention generally relates to a magnetic recording and/or reproducing apparatus for use with a flexible storage medium, such as a magnetic disk. More particularly, the invention relates to apparatus that provides a stable, i.e., substantially constant, transducer-to-medium relation for enhancing the recording or reproducing of information on the flexible medium.
2. Description of the Prior Art
Magnetic recording and/or reproducing may be divided into two general techniques. The first one is a "non-contacting" technique in which the storage medium, often a magnetic disk, and the transducer remain slightly spaced apart by a layer of air. The second one is a "contacting" technique in which the storage medium, often a magnetic tape, and the transducer are substantially in physical contact. For successfully recording or reproducing information on a magnetic medium, using either type of technique, particularly at high densities such as employed in a video recorder or computer equipment, the transducer-to-medium relation should remain constant over a wide range of operating parameters. Variations in the transducer-to-medium relation can have a significant effect on the fringing flux pattern and, therefore, the resolution of the sensing and recording of information on the magnetic medium. Unfortunately, with a magnetic medium, especially one that is flexible, as for example a floppy disk, the transducer-to-medium relation may be varied by the interaction of many parameters, such as temperature, humidity, relative speed between the medium and the transducer, penetration of the transducer into the medium, the contour of surface areas surrounding the transducer, flexibility and variations in thickness of the medium, the angles of attack and tilt of the transducer with respect to the medium, etc.
Various non-contacting type recording and/or reproducing apparatus have been proposed which seek to ensure a substantially constant spacing between a flexible magnetic disk and a magnetic head. For example, in U.S. Pat. No. 3,178,719, a flexible magnetic disk initially in close proximity (e.g., 0.005"-0.010") to a flat air bearing surface of an annular plate, usually referred to as a Bernoulli plate, is rotated at a relatively fast speed, which causes the rotated disk to assume a stable position at a small distance from the air bearing surface. It is believed that the stable position results from a balance of centrifugal and Bernoulli forces that causes the rotated disk to reach a condition of equilibrium closely spaced from the air bearing surface. A plurality of magnetic heads, radially disposed with respect to the rotated disk, are embedded in the Bernoulli plate, either slightly above or slightly below e.g., 0.002") or flush with the air bearing surface. Since the close spacing between the air bearing surface and the rotated disk, and therefore the critical spacing between the magnetic heads and the rotated disk, varies as a function of the disk radius, a vacuum pump is included to create a partial vacuum in respective round openings in the plate, which each contain one of the heads. The partial vacuum deforms small annular areas of the flexible disk around the magnetic heads to independently control the close spacing between each one of the heads and localized portions of the disk.
Although the non-contacting recording apparatus disclosed in U.S. Pat. No. 3,178,719 may perform satisfactorily, it requires the use of a vacuum pump to control the critical head-to-disk spacing, which increases the construction and operating costs of such apparatus. A simpler non-contacting recording apparatus that dispenses with the need for a vacuum pump is disclosed in U.S. Pat. No. 4,074,330. In that apparatus, an annular (Bernoulli) plate has a groove which is sealed at its ends, is open to a flexible disk, and is radially disposed with respect to the disk. A magnetic head, movable along the groove, projects from the groove to a location slightly above a flat air bearing surface of the plate facing the disk, to penetrate into the disk. Bracketing the groove, on either side of the head, is a pair of up-stream and down-stream convex surfaces which are radially coextensive with the groove. The respective apexes of the two convex surfaces are located closer to the flat air bearing surface of the plate than to the radially extending sides of the groove. With this arrangement, it is purported that the amount of air carried by the rotated disk out of the groove is greater than the amount of air carried by such disk into the groove. The net result is to exhaust air from the groove, which generates a Bernoulli pull down force on the rotated disk over the groove. Such pull down force is opposite to the tendency of the rotated disk to dimple away from the magnetic head because of penetration of the head into the disk, and therefore ensures a stable close spacing between the head and the disk.
The flat air bearing surfaces of the Bernoulli plates in the '719 and '330 patents, as well as in other non-contacting recording apparatus, such as disclosed in U.S. Pat. No. 4,003,091, are larger than the flexible disks with which they are used. This arrangement makes it impossible for such an air bearing surface to penetrate into a flexible disk jointly with a magnetic head, which prevents use of the apparatus in certain instances, for example with a disk that is housed in a cartridge. Moreover, the round vacuum-supplied opening in the '719 patent for deforming a flexible disk about a magnetic head, and the convex surfaces in the '330 and '091 patents for effecting pull down of a flexible disk against a magnetic head, are of respective configurations that may deform the flexible disk to such an extent that its useful life may be shortened.
When a flexible magnetic disk is housed in a cartridge, the situation becomes even more critical because the stability of the head-to-disk relation may be affected by certain surfaces of the cartridge proximate the rotated disk. Therefore, to ensure a stable head-to-disk relation in a disk cartridge it has been proposed to have the head contact the disk, as disclosed in U.K. Patent Application GB 2,101,391A, published Jan. 12, 1983 and in IEEE Transactions on Consumer Electronics, Vol. CE-28, No. 3, August 1982, p. 326. In that example, the disk cartridge includes an opposed pair of openings which extend radially on either side of the magnetic disk. As the flexible disk is rotated, a magnetic head is moved along one of the openings in the nominal plane of the disk to penetrate the disk, and a guide plate in the other opening limits the tendency of the rotated disk to lift off the magnetic head. Use of the guide plate ensures a stable, intimate head-to-disk contact. Without the guide plate, the head-to-disk relation becomes unstable and may vary to the extent that the signal-to-noise ratio will be unacceptable.
While such use of a guide plate with a magnetic head for achieving a stable head-to-disk contact in a cartridge may perform satisfactorily, the spacing between the head and the guide plate is especially critical, and therefore can be a problem. If the spacing is too small, the disk and the head will become degraded rather quickly by wear of the one against the other. If the spacing is too large, the head-to-disk relation will become unstable. As a result, the prior art has required that relatively expensive means be employed to establish the spacing and to maintain it with some degree of assurance, particularly after extended use of the head and the guide plate.